Waveguide for plastic welding, arrangement for plastic welding, a welding method as well as a manufacturing method of a waveguide

ABSTRACT

A waveguide for plastic welding has an entry end, an exit end as well as a first and a second inner face arranged between the entry end and the exit end, which are arranged opposite to each other and by means of which laser light can be reflected. A first distance between the entry end and the exit end defines a length of the waveguide and a second distance between the first and the second inner face defines a thickness of the waveguide. The exit end may be arranged opposite to the entry end and a central plane of the waveguide may extend centrally from the entry end to the exit end. The first inner face comprises a continuously curved, concave shape so that a third distance between the first inner face and the central plane varies continuously from the entry end in the direction of the exit end.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/284,714 filed on Feb. 25, 2019 and claims the priority of Germanpatent application No. DE102018104629.4, filed on Feb. 28, 2018. Theentire contents of these priority applications are incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure is related to a negative as well as a positivewaveguide for plastic welding, an arrangement for plastic welding, amethod for plastic welding as well as a manufacturing method of thewaveguide.

BACKGROUND

Generally, several types of waveguides for laser light for plasticwelding are known. Often, the last element of an arrangement for plasticwelding is denoted as waveguide, before the laser light of a laser lightsource enters the components to be welded. The waveguide has at thatespecially the object to homogenize the distribution of the laser lightso that the energy of the laser light enters the components to be weldedas uniformly as possible and individual focal points are avoided.

At that, it is generally differentiated between two types of waveguide,namely the positive and the negative waveguides. Positive waveguidesconsists of a solid state which guides laser light in the interiorfollowing the law of total internal reflection. An example of such apositive waveguide is described in DE 10 2004 058 221 A1. Negativewaveguides have the feature of a channel like cavity, which is coatedwith a reflective layer and in which the laser light is guided. Anexample of such a negative waveguide is described in DE 11 2007 002 109T5. The negative waveguide described there has a non-conicallongitudinal cross-section producing a non-circular weld zone. Further,negative waveguides having a conical longitudinal cross-section are alsoknown.

With respect to the waveguide as usually last element of a weldingarrangement prior to the components to be welded to each other it isthus desirable that energy losses due to the waveguide are kept as smallas possible.

It is thus an object of the present invention to provide a waveguide atwhich the energy losses caused by the waveguide are smaller compared tothe known waveguides and the waveguide provides a better energydistribution at the components to be welded to each other. Further, itis an object of the present invention to provide a respectivearrangement, a respective welding method as well as respectivemanufacturing methods of the waveguide.

SUMMARY

A first negative waveguide for plastic welding, especially for lasertransmission welding, comprises: an entry end defining an entry face forlaser light, an exit end defining an exit face for laser light as wellas a first and a second inner face which are arranged between the entryend and the exit end, which are arranged opposite to each other and bymeans of which laser light can be reflected, wherein a first distancebetween the entry end and the exit end defines a length of the waveguideand a second distance between the first and the second inner facedefines a thickness of the waveguide, wherein the exit end is arrangedopposite to the entry end and a central plane of the waveguide extendscentrally from the entry end to the exit end, and the first inner facecomprises a continuously curved, concave shape so that a third distancebetween the first inner face and the central plane of the waveguidevaries continuously from the entry end in the direction of the exit end.

The first negative waveguide is described in the following as part ofits usage in an arrangement for plastic welding, especially in anarrangement for laser transmission welding. Laser transmission weldingis a one-step process in which the heating of the components to bewelded and the joining process take place almost at the same time. Forthis process, one of the components to be welded must have a hightransmittance or transmission degree in the range of the laser wavelength and the other must have a high absorptance or absorptivity. Priorto the welding process, both components are positioned in the desiredend position and the joining pressure is applied. The laser beamradiates or shines through the transparent component withoutconsiderable heating. At first in the absorption component the laserbeam is absorbed in a surface near layer, wherein the laser energy isconverted in thermal energy and the absorption component is melted atthese places. Due to thermal conduction processes, also the transparentcomponent is plasticized in the area of the joining zone. By means ofthe joining force applied from the outside as well as the inner joiningpressure resulting from the expansion of the plastic melt, an adhesivebond connection of the two components is achieved. Here, it may bepreferred to use the first negative waveguide as part of a simultaneouslaser transmission welding which is subsequently also denoted assimultaneous welding.

At the simultaneous welding, the whole welding contour or seam contourof the components to be welded to each other may be irradiated at thesame time. This ensures an extreme reduction of the process times andmakes a bridging of the clearances possible by means of melting away.Additionally, the welding seam is stronger compared to the contourwelding in which a laser beam is guided along the seam as thesimultaneous welding has a higher interaction time.

During the operation of a respective arrangement for plastic welding,especially for laser transmission welding, laser light runs from a laserlight source through an often flexible light guide or a bundle offlexible light guides which is coupled at its end facing away from thelaser light source to the waveguide. The laser light exits thus thelight guide or the bundle of light guides and enters the waveguide, ishomogenized in the waveguide and impinges on the components to be weldedthereafter.

As has been outlined at the beginning, the negative waveguide is markedby a cavity through which the laser light is guided. Usually, thenegative waveguide has a channel like design or construction. The firstnegative waveguide comprises the entry end, the exit end, a firstreflecting inner face and a second reflecting inner face opposite to thefirst inner face. The entry face of the entry end is defined especiallyby the plane in which the first ends of the first and second inner facesat the entry end of the waveguide are arranged. Advantageously the laserlight enters the waveguide at the entry end perpendicular to the entryface. The exit end with the exit face is thus respectively andpreferably defined by the plane in which the second ends of the firstand second inner face at the exit end of the waveguide are arranged. Ina further embodiment, the exit face and the entry face are arranged inplanes which extend parallel to each other.

The exit end may be adapted to a desired seam contour of the componentsto be welded. For example, and in the case of two longitudinalcomponents to be welded to each other, the waveguide has a longitudinalshape transverse to the direction of the laser light passing through thewaveguide. An extension of the first negative waveguide in thisdirection is also defined as width. According to a further example andin case two annular shaped components have to be welded to each other,the exit end and thus also the exit face are also annular.

Furthermore, the central plane of the waveguide extends centrallybetween the entry end and the exit end in the direction of the laserlight starting from the entry end to the exit end. Centrally from theentry end to the exit end refers here to the geometric center of therespective end or the respective face. With respect to the exemplarilyfirst negative waveguide having a longitudinal shape transverse to thedirection of the laser light, the thickness, i.e. the second distancebetween the inner faces, is at the entry end as well as at the exit endfor example 5 mm. The central plane would then have a distance to thefirst and the second inner face of 2.5 millimeters at the entry end andat the exit end, which will be discussed below with respect to thedetailed description of a preferred embodiment. According to anotherexample, the thickness is equal at the entry end as well as at the exitend and may be below 3 mm, or below 2.8 mm. In an alternative, thethickness at the entry end may be larger compared to the thickness atthe exit end. For example, the thickness at the entry end may be between2.2 to 2.8 mm whereas the thickness at the exit end is 1.4 mm.

According to the disclosure, the first inner face comprises thecontinuously curved, concave shape. In the cross-section of thewaveguide, the first inner face is thus curved to the outside. Thiscontinuously curved concave shape may be part of an ellipse. Due to thisdesign or shaping of the first inner face, the third distance betweenthe first inner face and the central plane of the waveguide variescontinuously from the entry end in the direction of the exit end. Thesecond inner face extends in a first alternative in a straight line. Inother embodiments, the second inner face has other shapes, may also be acontinuously curved shape, which is formed by a plurality of straightsegments or which is part of an ellipse, for example of a secondellipse. At the exemplarily straight-lined design of the second innerface, a fourth distance between the central plane and the second innerface is constant or invariable, wherein not only the third distance butalso the thickness of the waveguide varies continuously due to the shapeof the first inner face.

In other embodiments, the first negative waveguide is a section of awaveguide portion or an integral part of a waveguide. For example, priorto the entry end and/or after the exit end, a further straight-linedwaveguide is present. The first entry end begins in this case where thefirst inner face starts having a concave shape. Accordingly, the exitend is present where the first inner face ends having a concave shape.

An advantage of this construction is that the beams of the laser lighthave less interaction with each other in the waveguide compared to awaveguide with straight inner faces. Further, the laser light can bebundled more powerful at the exit end by means of the inventive firstnegative waveguide. By means of the first negative waveguide, anespecially homogeneous power density distribution can thus be achievedat the welding seam. In this way, a larger tolerance between waveguideand the components to be welded can be compensated which increases thesimplicity of the usage of an arrangement using the inventive firstnegative waveguide. Especially, tolerances of up to ±1 mm betweenwaveguide and the desired welding seam of the components to be weldedcan be compensated by means of the first negative waveguide.Furthermore, the first negative waveguide allows the transit of moreenergy compared to a straight waveguide. This applies also, in case thesurface of the waveguide is not polished.

A first positive waveguide for plastic welding, especially for lasertransmission welding, comprises: an entry end defining an entry face forlaser light, an exit end defining an exit face for laser light as wellas a first and a second inner face which are arranged between the entryend and the exit end, which are arranged opposite to each other and bymeans of which laser light can be reflected, wherein a first distancebetween the entry end and the exit end defines a length of the waveguideand a second distance between the first and the second inner facedefines a thickness of the waveguide, wherein the exit end is arrangedopposite to the entry end and a central plane of the waveguide extendscentrally from the entry end to the exit end, and the first inner facecomprises a continuously curved, concave shape so that a third distancebetween the first inner face and the central plane of the waveguidevaries continuously from the entry end in the direction of the exit end.

The above statements regarding the first negative waveguide applyanalogously to the first positive waveguide. A difference between thefirst negative waveguide and the first positive waveguide is that thepositive waveguide consists of a solid state or solid body. The solidstate comprises the entry end and the exit end. The first and the secondinner face are formed by a first and a second inner side of a first anda second side face of the solid state. The material of the solid stateis chosen such that in the interior of the solid state and especially atthe first and the second inner face total reflection occurs. Theadvantages which can be achieved by means of the first positivewaveguide correspond thus to the advantages which can be achieved withthe inventive first negative waveguide. Further, by means of thepositive waveguide, the energy can be transferred through the waveguideto the parts to be welded without refraction. Additionally, the positivewaveguide is specifically useful in applications having, for example,limited installation space. Further, pressure can be applied directly tothe work pieces to be welded by means of the positive waveguide, forexample when welding thin sheets of one material to another material.

In a further embodiment of the first negative and the first positivewaveguide, the third distance increases or decreases continuously fromthe entry end in the direction of the exit end. If the third distanceincreases from the entry end in the direction of the exit end, thethickness at the entry end is smaller compared to the exit end. If thethird distance decreases from the entry end in the direction of the exitend, the thickness at the entry end is larger compared to the exit end.In this context, it may be preferred if the third distance firstincreases continuously from the entry end in the direction of the exitend up to an apex or vertex and thereafter decreases continuously. Thismeans, with respect to the third distance, that the third distance firstincreases from the entry end in the direction of the exit end up to theapex and then decreases. Here, also different constructions arepossible. According to an example, the thickness at the entry end islarger or smaller compared to the exit end. According to a furtherembodiment, the thickness at the exit end corresponds to the thicknessat the entry end. Thus, the exit end as well as the entry end can bespecifically adapted to the respective requirements and it results anespecially large range use for the first negative and the first positivewaveguide.

In a further embodiment of the first negative and the first positivewaveguide, the second inner face is formed mirror-symmetrically to thefirst inner face. The central plane of the waveguide is used as mirrorplane. In this way, the second inner face is constructed like the firstinner face so that both have a continuously curved concave shape. Afourth distance between the second inner face and the central plane ofthe waveguide varies thus from the entry end in the direction of theexit end also continuously. Especially, the thickness of the waveguidevaries in this way continuously, and the thickness may increase from theentry end in the direction of the exit end up to an apex and thereafterdecrease. By means of this mirror-symmetrical configuration, theinteraction between the laser beams in the waveguide is furtherdecreased and the power density distribution in the weld seam is alsofurther improved.

In a further embodiment of the first negative and the first positivewaveguide, the thickness at the entry end is between 8% and 25%,preferably 10% to 20% of the length of the waveguide. Additionally oralternatively, the third distance may increase from the entry end in thedirection of the exit end up to an apex and decreases thereafter,wherein the apex is arranged with respect to the length in a rangebetween ¼ and ¾ of the length of the waveguide, preferably in a rangebetween ⅓ and ⅔ and especially preferred at about ½. Further, thethickness at the exit end corresponds or may be equal to the thicknessat the entry end. It also may be preferred that the third distanceincreases from the entry end in the direction of the exit end up to anapex and decreases thereafter and the thickness in the apex is about1.2- to 2-times, preferably 1.4- to 1.8-times and especially preferred1.6-times the thickness at the entry end. In a further embodiment, thesecond inner face is mirror symmetrical to the first inner face, asexplained above. Each of these features taken alone realizes animprovement of the power density distribution in the welding seam of thecomponents to be welded.

According to a further embodiment, the continuously curved concave shapeof the first inner face is part of an ellipse. In case of amirror-symmetrical configuration of the second inner face, this appliesalso to the second inner face. In case of a non-mirror-symmetricalconfiguration of the second inner face, the second inner face may have acontinuously curved shape which is part of a second, further ellipse. Anellipse has a large axis and a small axis. The apexes on the large axisare denoted as main vertexes and the apexes on the small axis aredenoted as sub-vertexes or auxiliary vertexes. The foci of the ellipse,i.e. the first and the second focal point, are arranged on both sides ofthe central point of the ellipse on the large axis. The ellipse is thusdefined as the geometrical place of all points for which the sum of thedistances from the foci, i.e. the sum of the focal radii, is constantlyequal to the distance between the main vertexes. With respect to theabove discussed embodiments with vertex, the vertex may correspond to asub-vertex of the ellipse. Due to this, a more longitudinal shapingresults in the cross-section of the waveguide, which supports thetransmission and homogenization of the laser light advantageously.Generally, due to the usage of a part or section of an ellipse, theinteraction between laser beams and the inner faces of the waveguide isfurther reduced, especially compared to a straight-lined waveguide. Thisapplies especially if the second inner face is formed mirror-symmetricalto the first inner face. Particularly by means of this embodiment, moreenergy can be transferred through the waveguide compared to a straightwaveguide. This applies also, in case the surface of the waveguide isnot polished.

An second negative waveguide for plastic welding, especially for lasertransmission welding comprises: an entry end defining an entry face forlaser light, an exit end defining an exit face for laser light as wellas a first and a second inner face which are arranged between the entryend and the exit end, which are arranged opposite to each other and bymeans of which laser light can be reflected, wherein a first distancebetween the entry end and the exit end defines a length of the waveguideand a second distance between the first and the second inner facedefines the thickness of the waveguide, and the first inner facecomprises a continuously curved concave shape which is part of a firstspiral, especially a first natural spiral, so that a radius of the firstspiral from a point of origin of the first spiral to the first innerface varies continuously along the waveguide.

With respect to the term of the negative waveguide as well as the lasertransmission welding, it is referred to the above illustrations withrespect to the inventive first negative waveguide. The second negativewaveguide can be used in an arrangement for plastic welding analogouslyto the first inventive waveguide. Differences between the first negativewaveguide and the second negative waveguide are the shaping of the firstinner face as well as the arrangement of the entry end with respect tothe exit end.

In contrast to the first negative waveguide, the entry end of the secondnegative waveguide has not to be arranged opposite to the exit end. Itis rather decisive that the first inner face has the continuously curvedconcave shape which is part of the first spiral. A spiral astwo-dimensional figure is generally defined in that the radius of thespiral from its point of origin varies continuously. This distinguishesthe spiral for example from a circle in which the radius is alwaysconstant. The radius of the first spiral varies or changes due to thedesign of the first inner face from its point of origin to the firstinner face along the waveguide continuously, which will be discussedlater within the detailed description of a preferred embodiment.

The second inner face may extend between the entry end and the exit endstraightly or in straight segments. In an alternative, the second innerface can also be formed curved. In the configuration with straightsegments as well as in the curved configuration, it may be preferredthat the space between the first and second inner face is not largerthan the space in case of a second inner face extending straightlybetween entry end and exit end. A curvature of the second inner facethus may be convex.

An advantage of the second negative waveguide is that lower energylosses occur in the interior of the waveguide and the laser light can beguided especially effectively through the waveguide to a welding seam.Thereby, and compared to known waveguides, more welding energy isprovided at the weld seam of the components to be welded to each other,especially if the components have an undercut at the welding seam.Further, and with respect to a closed angular or cornered shape of thewaveguide, especially at the corners of the entry end a collision of thelight guides can be avoided due to the spiral shape of the first innerface in this area. This makes the arrangement more simply usablecompared to the known arrangements.

An second positive waveguide for plastic welding, especially for lasertransmission welding comprises: an entry end defining an entry face forlaser light, an exit end defining an exit face for laser light as wellas a first and a second inner face which are arranged between the entryend and the exit end, which are arranged opposite to each other and bymeans of which laser light can be reflected, wherein a first distancebetween the entry end and the exit end defines a length of the waveguideand a second distance between the first and the second inner facedefines the thickness of the waveguide, and the first inner facecomprises a continuously curved concave shape which is part of a firstspiral, especially a first natural spiral, so that a radius of the firstspiral from a point of origin of the first spiral to the first innerface varies continuously along the waveguide.

The above illustrations with respect to the second negative waveguideapply analogously to the second positive waveguide. With respect to theconstruction of a positive waveguide compared to a negative waveguide,it is referred to the above explanation for the first positivewaveguide, which apply also to the second positive waveguide. Insummary, the advantages which can be achieved with the second positivewaveguide correspond thus to the advantages which can be achieved withthe second negative waveguide.

In a further embodiment of the second negative and the second positivewaveguide, the radius of the first spiral increases or decreasescontinuously from the point of origin of the first spiral to the firstinner face along the waveguide from the entry end to the exit end. Inthis way, curvatures of the first inner face of the waveguide which areadapted to the respective case of application are obtainable.

Further, an angle in the range of 30° to 150°, preferably 40° to 120°may be enclosed between the entry end and the exit end, especiallybetween the entry face and the exit face. The laser light from the lightguide may enter the waveguide perpendicular to the entry face and exitsthe waveguide perpendicular to the exit surface. Based on the desiredangle for the respective case of application, for example due toundercuts being present at the components to be welded, as well as onthe available installation space, the desired section of the spiral canbe chosen to realize the concave shape of the first inner face.

In a further embodiment, a central plane is defined between the firstand the second inner face, the distance of which is constant to thefirst and the second inner face along the length of the waveguide sothat the second inner face also has a continuously curved shape. Thisshape of the second inner face is part of a second spiral, especially asecond natural spiral so that a radius of the second spiral from a pointof origin of the second spiral to the second inner face variescontinuously along the wave guide. Due to this configuration, the laserlight can be guided very effectively within the waveguide.

Further, the thickness of the waveguide may decrease continuously fromthe entry end in the direction of the exit end. In this way, a furtherfocus effect of the laser light from the entry end in the direction ofthe exit end is achieved.

The concave continuously curved shape, which is part of a spiral, may bechosen from one of the following spiral types: hyperbolic, Archimedean,logarithmic or from a spiral based on the Fibonacci-sequence. TheFibonacci-sequence is the sequence (F_(n))_(n∈N) with F₁=F₂=1 andF_(n+2)=F_(n)+F_(n+1). The spiral based on the Fibonacci-sequence is asubset of the logarithmic spiral. By means of this configuration, laserlight can be guided through the waveguide with very low losses,especially to an undercut of the components to be welded.

A curve which intersects all beams starting from the point of origin 0in the same angle α is defined as logarithmic spiral. In case of thelogarithmic spiral and if a sub-section of the spiral is present, thepoint of origin can be determined when the angle α is known. As a spiralis a two-dimensional figure, the waveguide has to be viewed here incross-section. A direction vector of the straight line extends in thiscase from the first inner face in the direction of the second innerface. If the shape of the second inner face is also based on a spiral,the direction vector of the respective straight line shows away from thefirst inner face.

A third negative waveguide for plastic welding, especially for lasertransmission welding comprises: an entry end defining an entry face forlaser light, an exit end defining an exit face for laser light as wellas a first and a second inner face which are arranged between the entryend and the exit end, which are arranged opposite to each other and bymeans of which laser light can be reflected, wherein a first distancebetween the entry end and the exit end defines a length of the waveguideand a second distance between the first and the second inner facedefines the thickness of the waveguide, and the first inner facecomprises a continuously curved concave shape which is part of a firstcurve. Especially, the first curve may be defined by a circle, aparabola, an exponential function or any other curve. Accordingly, thecurved concave shape may be part of a circle, a parabola or anexponential function. With respect to further features and theadvantages, it is referred to the inventive second negative waveguide.

A third positive waveguide for plastic welding, especially for lasertransmission welding comprises: an entry end defining an entry face forlaser light, an exit end defining an exit face for laser light as wellas a first and a second inner face which are arranged between the entryend and the exit end, which are arranged opposite to each other and bymeans of which laser light can be reflected, wherein a first distancebetween the entry end and the exit end defines a length of the waveguideand a second distance between the first and the second inner facedefines the thickness of the waveguide, and the first inner facecomprises a continuously curved concave shape which is part of a firstcurve. Concerning further possible features, it is referred to the thirdnegative waveguide as well as the second positive waveguide. Inparticular, and with respect to the advantages, it is referred to thesecond positive waveguide.

An arrangement for plastic welding, especially for laser transmissionwelding, comprises: a laser light source, a light guide, which may be aplurality of light guides, and a waveguide, wherein in the operation ofthe arrangement the laser light passes from the laser light sourcethrough the light guide and subsequently through the waveguide. Thearrangement uses the above-described inventive waveguide so that theabove-described advantages for the respective waveguide applyanalogously to the arrangement.

In an advantageous embodiment of the arrangement and upon usage of thesecond negative or positive waveguide, a length of the first inner faceof the second or third negative or positive waveguide is in the range of3-times to 4-times, especially of 3.5-times, of a distance between theindividual light guides from the plurality of light guides. In this way,an especially compact construction of the waveguide can be achieved.

A method for plastic welding, especially for laser transmission welding,with an arrangement comprises the following steps: arranging two plasticcomponents to be welded to each other in a mounting device, creatinglaser light by means of a laser light source, wherein the laser lightpasses through the light guide, may be a plurality of light guides, andsubsequently through a waveguide, and welding the plastic components tobe welded to each other by means of the laser light exiting thewaveguide.

A first manufacturing method is related to the manufacturing of thefirst, second or third negative waveguide. The first manufacturingmethod comprises the steps of: providing a first and a second innerface, applying a reflecting layer on the first and the second innerface, arranging the first and the second inner face such that they areopposite to each other, wherein a first end of the first and the secondinner face define an entry end of the waveguide, which defines an entryface for laser light, and a second end of the first and the second innerface define an exit end of the waveguide, which defines an exit face forlaser light, wherein a first distance between the entry end and the exitend defines a length of the waveguide and a second distance between thefirst and the second inner face defines a thickness of the waveguide,wherein the exit end is arranged opposite to the entry end and a centralplane of the waveguide extends centrally from the entry end to the exitend while the first inner face has a continuously curved concave shapeso that a third distance between the first inner face and the centralplane of the waveguide varies continuously from the entry end in thedirection of the exit end or the first inner face has a continuouslycurved concave shape which is part of a first spiral, especially a firstnatural spiral so that the radius of the first spiral variescontinuously from a point of origin of the first spiral to the firstinner face along the waveguide or the first inner face has acontinuously curved concave shape which is part of a first curve. Bymeans of the manufacturing method, the first, second and third negativewaveguide can be manufactured so that it is referred to the aboveexplanations for the respective first, second and third negativewaveguide with respect to the respective advantages.

A second manufacturing method is related to the manufacturing of thefirst or second positive waveguide. The second manufacturing methodcomprises the steps of: providing a solid state of a light guidingmaterial, wherein the solid state comprises an entry end defining anentry face for laser light and an exit end defining an exit face forlaser light, wherein the solid state has a first side face defining afirst inner face and a second side face defining a second inner facewherein the first and the second inner face are arranged opposite toeach other and the solid state consists of a material which provides atotal reflection of laser light at the first and the second inner facewhile a first distance between the entry end and the exit end defines alength of the waveguide and a second distance between the first and thesecond inner face defines a thickness of the waveguide, wherein the exitend is arranged opposite to the entry end and a central plane of thewaveguide extends centrally from the entry end to the exit end and themethod comprises the step of: forming the first side face such that thefirst inner face has a continuously curved concave shape so that a thirddistance between the first inner face and the central plane of thewaveguide varies continuously from the entry end in the direction of theexit end or the method comprises the further step of: forming the firstside face such that the first inner face has a continuously curvedconcave shape which is part of a first spiral, especially a firstnatural spiral, so that a radius of the first spiral from a point oforigin of the first spiral to the first inner face varies continuouslyalong the waveguide or the method comprises the further step of: formingthe first side face such that the first inner face has a continuouslycurved concave shape which is part of a first curve. By means of thesecond manufacturing method, the inventive first, second and thirdpositive waveguide can be manufactured so that it is referred to theabove statements for the respective first, second and third positivewaveguide with respect to the respective advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present disclosure will be described in detailbased on the drawings. In the drawings, the same reference signs denotethe same elements and/or components. It shows:

FIG. 1 shows an embodiment of an arrangement for plastic welding with anembodiment of the first negative waveguide in a perspective view,

FIG. 2 is a cross-section of the embodiment of the first negativewaveguide according to FIG. 1,

FIG. 3a shows the course of laser light in a straight negative waveguideaccording to the prior art in a cross-sectional view at precisealignment of the waveguide with the welding seam,

FIG. 3b shows the course of laser light in an embodiment of the firstnegative waveguide according to FIG. 1 in a cross-sectional view atprecise alignment of the waveguide with the welding seam,

FIG. 4a shows the course of laser light in a straight negative waveguideaccording to the prior art in a cross-sectional view at a displacementof 0.5 mm of the waveguide with respect to the welding seam,

FIG. 4b shows the course of laser light in the embodiment of the firstnegative waveguide according to FIG. 1 in a cross-sectional view at adisplacement of 0.5 mm of the waveguide with respect to the weldingseam,

FIG. 5a shows the course of laser light in a straight negative waveguideaccording to the prior art in a cross-sectional view at a displacementof 1.0 mm of the waveguide with respect to the welding seam,

FIG. 5b shows the course of laser light in the embodiment of the firstnegative waveguide according to FIG. 1 in a cross-sectional view at adisplacement of 1.0 mm of the waveguide with respect to the weldingseam,

FIG. 6a shows the course of laser light after the component to be weldedwhen using a straight negative waveguide according to the prior art,

FIG. 6b shows the course of the laser light after the component to bewelded when using the embodiment of the first negative waveguideaccording to FIG. 1,

FIG. 7a is an enlarged view of a section of FIG. 6 a,

FIG. 7b is an enlarged view of a section of FIG. 6 b,

FIG. 8a is a cross-section of a straight negative waveguide according tothe prior art with two laser beams for clarifying the interaction of thelaser beams with each other,

FIG. 8b is a cross-section of the embodiment of the first negativewaveguide according to FIG. 1 with two laser beams for clarifying theinteraction of the laser beams with each other,

FIG. 9 is a perspective view of an arrangement for plastic welding witha section through an embodiment of a second negative waveguide accordingto the present invention,

FIG. 10 shows a course of laser light through the embodiment of thesecond negative waveguide according to FIG. 9,

FIG. 11 is a cross-sectional view of the embodiment of the secondnegative waveguide according to FIG. 10,

FIG. 12 shows an enlarged view of a section of FIG. 11,

FIG. 13 is a schematic depiction of the usage of the embodiment of thesecond negative waveguide for avoiding a collision of light guides inthe cornered area,

FIG. 14 is an overlapping view of a waveguide according to the prior artand the embodiment of the second negative waveguide,

FIG. 15 is a flow chart of an embodiment of a welding method,

FIG. 16 is a flow chart of an embodiment of a manufacturing method of anegative waveguide, and

FIG. 17 is a flow chart of an embodiment of a manufacturing method of apositive waveguide.

DETAILED DESCRIPTION

Generally, the waveguides described in the following can be used in anyprocess in which laser light has to be guided to a welding zone.Exemplarily, the usage of the waveguide is explained in an arrangementfor plastic welding, especially for laser transmission welding. Forreasons of clarity, also the embodiments of the negative waveguideaccording to the present disclosure are described, wherein therespective embodiments apply analogously to positive waveguides.Furthermore, the embodiments described in the following must not definean individual waveguide but may be a section of a waveguide portion oran integral part of a waveguide. According to an example, an especiallystraight-lined waveguide is present prior to the entry end and/or afterthe exit end. The first entry end is present in this case where thefirst inner face starts having a concave shape. Accordingly, the exitend is present where the first inner face ends having a concave shape.

At the laser transmission welding, a first component of plastic, whichis often denoted as transmission component, is welded to a secondcomponent, which is often denoted as absorption component, by means oflaser light and with the application of pressure. The transmissioncomponent or a portion of the transmission component is arrangedadjacent to the waveguide as the laser beam shines through it withoutconsiderable heating. The absorption component or a portion of theabsorption component is arranged on the side of the transmissioncomponent or the portion of the transmission component which is oppositeto the waveguide. At first in the absorption component the laser lightis absorbed in a surface near layer, wherein the laser energy isconverted in thermal energy and the absorption component is melted atthese places. The waveguide is used for example for applying thenecessary joining pressure. Due to thermal conduction processes, alsothe transparent component is plasticized in the area of the joiningzone. By means of the joining pressure applied from the outside as wellas the inner joining pressure resulting from the expansion of theplastic melt, an adhesive bond connection of the two components isachieved. Here, it may be preferred to use the negative and positivewaveguides as part of a simultaneous laser transmission welding. In thismethod, the whole welding contour or seam contour of the components tobe welded to each other may be irradiated at the same time. This ensuresan extreme reduction of the process times and makes a bridging of theclearances possible by means of melting away. Additionally, the weldingseam is stronger compared to the contour welding in which a laser beamis guided along the seam as the simultaneous welding has a higherinteraction time.

Now referring to FIG. 1, an embodiment of an arrangement 1 for plasticwelding with an embodiment of a first negative waveguide 20 is shown ina perspective view. In the arrangement 1, laser light is guided from alaser light source via a plurality of preferably flexible light guides10 to the waveguide 20. The light guides 10 are connected at an entryend 22 with the waveguide 20. The laser light is guided through thewaveguide 20 to the components to be welded, one component 15 of whichis exemplarily shown. At that, it is one object of the waveguide 20 tohomogenize the laser light from the light guides so that the powerdensity distribution of the laser light in the welding zone or weldingseam is as uniformly as possible.

Additionally referring to FIG. 2, which shows a cross sectional view ofthe embodiment of the first negative waveguide according to FIG. 1, theconstruction of the waveguide 20 is described. The waveguide 20comprises the entry end 22 defining an entry face for the laser light.Opposite to the entry end 22, the waveguide 20 comprises an exit end 24defining an exit face for the laser light. A first 26 and a second innerface 28 extend between the entry end 22 and the exit end 24. The twoinner faces 26 and 28 are arranged opposite to each other and reflectthe laser light during operation of the arrangement 1.

The entry face of the entry end 22 is defined by the plane in which thefirst ends of the first 26 and second inner face 28 are arranged at theentry end 22 of the waveguide 20. In the embodiment shown, the laserlight enters the waveguide 20 perpendicular to the entry face at theentry end 22. The exit end 24 with the exit face is defined, analogouslyto the entry face, by the plane in which the second ends of the first 26and the second inner face 28 are arranged at the exit end of thewaveguide 20. In the embodiment shown, the exit face and the entry faceare arranged in planes which extend parallel to each other.

The exit end 24 is adapted in the embodiment shown to a desired seamcontour of the components 15 to be welded so that the waveguide 20 has alongitudinal shape transverse to the direction of the laser lightpassing through the waveguide 20. An extension of the first negativewaveguide in this direction is defined as width. In an alternativeembodiment, the exit face has another shape. For example, the exit endand thus also the exit face are annular to weld two annular componentsto each other. In this case, the entry end and the entry face are formedanalogously so that they are still arranged opposite to the exit end andthe exit face.

Due to the configuration of the waveguide 20 as negative waveguide 20, acavity is present between the two inner faces 26 and 28 and the twoinner faces are provided with a reflecting layer. Usually, the negativewaveguide 20 has thus a channel like shape. In case of a positivewaveguide consisting of a solid state, no cavity would be presentbetween the two inner faces. At the respective positive waveguide, it isensured by the choice of the appropriate material that total reflectionoccurs in the interior of the waveguide, especially at the inner faces.

A first distance between the entry end 22 and the exit end 24 defines alength L of the waveguide 20. A second distance between the first 26 andthe second inner face 28 defines a thickness D of the waveguide.Further, a central plane M of the waveguide 20 extends centrally fromthe entry end 22 to the exit end 24. Centrally from the entry end 22 tothe exit end 24 refers here to the geometric center. With respect to thewaveguide 20 shown having a longitudinal shape transverse to thedirection of the laser light, the thickness D, i.e. the second distancebetween the inner faces 26, 28, is at the entry end 22 as well as at theexit end 24 for example 5 mm. The central plane M would then have adistance to the first 26 and the second inner face 28 of 2.5millimeters. In this example, it is assumed that the thickness at theexit end 24 corresponds or is equal to the thickness at the entry end22. Other configurations are possible so that the thickness at the entryend 22 is larger or smaller compared to the exit end 24 in otherembodiments.

As can be seen especially from FIG. 2, the first inner face 26 comprisesa continuously curved, concave shape. In the cross-section of thewaveguide 20, the first inner face 26 is thus curved to the outside. Inthe embodiment shown, this continuously curved concave shape is part ofan ellipse. Due to this configuration of the first inner face 26, athird distance D₁ between the first inner face 26 and the central planeM of the waveguide 20 varies continuously from the entry end 22 in thedirection of the exit end 24.

In the embodiment shown, the second inner face 28 is formed mirrorsymmetrical to the first inner face 26. The central plane M of thewaveguide 20 servers as mirror plane. In this way, the second inner face28 is constructed like the first inner face 26 so that both have aconcave shape. A fourth distance D₂ between the second inner face 28 andthe central plane M of the waveguide 20 varies thus also continuouslyfrom the entry end 22 in the direction of the exit end 24. Other shapesof the second inner face 28 can also be realized, as for example astraight shape or a shape consisting of a plurality of straightsegments.

As can be also seen in FIG. 2, the third distance D₁ first increasescontinuously from the entry end 22 in the direction of the exit end 24up to an apex or vertex S₁ and thereafter decreases continuously. Due tothe mirror symmetrical configuration, this applies also to the secondinner face 28 which has a second vertex S₂. By means of this mirrorsymmetrical configuration, the interaction between the laser beams inthe waveguide 20 is further reduced and the power density distributionin the welding seam is also further increased, which will be explainedin detail based on the following FIGS. 3a to 8 a.

The continuously curved, concave shape of the first inner face 26 andthus also of the second inner face 28 is part of an ellipse. An ellipsehas a large axis and a small axis. In the embodiment shown, the largeaxis lies in the central plane M and the small axis extends through thevertexes S₁ and S₂. The apexes on the large axis are denoted as mainvertexes and the apexes on the small axis, here the vertexes S₁ and S₂,are denoted as sub-vertexes or auxiliary vertexes. The central point ofthe ellipse is in the point of intersection of the large and the smallaxis. The foci of the ellipse are arranged on both sides of the centralpoint of the ellipse on the large axis, i.e. the first and the secondfocal point. The foci are thus arrange in the central plane M.

The ellipse is defined as the geometrical place of all points for whichthe sum of the distances from the foci, i.e. the sum of the focal radii,is constantly equal to the distance between the main vertexes. Thisdefinition is reproduced in the following equation (7). For the ellipse,the following equations apply:

$\begin{matrix}{{\frac{x^{2}}{a^{2}} + \frac{y^{2}}{b^{2}}} = 1} & (1) \\{x = {a*{\cos(t)}}} & ( {2a} ) \\{y = {b*{\sin(t)}}} & ( {2b} ) \\{c = \sqrt{a^{2} - b^{2}}} & (3) \\{e = \frac{c}{a}} & (4) \\{r_{1} = {a - {e*x}}} & (5) \\{r_{2} = {a + {e*x}}} & (6) \\{{r_{1} + r_{2}} = {2{a.}}} & (7)\end{matrix}$

It is:

x, y the coordinates of a point on the ellipse,

a the distance between main vertex and central point of the ellipse,

b the distance between sub-vertex and central point of the ellipse,

t angle starting from a main vertex,

c distance between the foci,

e orbital eccentricity of the ellipse,

r₁ focal radius of the first focal point and

r₂ focal radius of the second focal point.

In the embodiment shown, the thickness D at the entry end is about 15%of the length L of the waveguide 20. Advantageous are values between 8%and 25%, preferably 10% to 20% of the length of the waveguide 20. Thevertexes S₁ and S₂ are arranged at the half of the length L. Here, thearrangement of the vertexes in a range between ¼ and ¾ of the length ofthe waveguide 20 is advantageous, wherein the arrangement in a rangebetween ⅓ and ⅔ is preferred. The thickness in the vertex is in theembodiment shown 1.6-times the thickness at the entry end 22, whereinvalues between 1.2-times to 2-times are advantageous and values between1.4-times and 1.8-times are preferred. Each of these features takenalone realizes an improvement of the power density distribution in thewelding seam of the components to be welded.

For an exemplarily calculation and based on the above relations, thefollowing is assumed:

thickness D at the entry end and at the exit end: 5 mm thickness D atthe vertexes S₁ and S₂: 8 mm and length L of the waveguide: 33.33 mm.

From this, the following known values for the ellipse result:

b: 4 mm first point (x, y): +16.67 mm, +2.5 mm second point (x, y):−16.67 mm, +2.5 mm third point (x, y): +16.67 mm, −2.5 mm third point(x, y): +16.67 mm, −2.5 mm

The positive y-values of 2.5 mm at the x-values+16.67 mm and −16.67 mmbelong to the first inner face 26 and the negative y-values belong tothe second inner face 28, respectively. In the following, the firstpoint (16.67 mm, 2.5 mm) is used for calculating the ellipse. As thethickness at the entry end 22 and at the exit end 24 are equal and theinner faces 26, 28 are mirror symmetrical, this single point issufficient to calculate the ellipse based on the above known values andthus to calculate the course of the first 26 and the second inner face28.

First, the equation (2b) is solved for sin(t), wherein a value of 0,625results for sin(t). The value fort is thus 0.675, which corresponds toan angle of 38.68°. The value for t=0,675 is plugged in equation (2a),which is solved for a. From this, a value for a of 21.35 mm results sothat the main vertexes are 42.70 mm apart. The distance between the fociaccording to equation (3) is thus c=20.98 mm. The foci are thus arrangedon the x-axis at values of +10.49 mm and −10.49 mm. As orbitaleccentricity a value of e=0.982 results according to equation (4). Basedon this, the parameters of the ellipse are now known.

Now referring to FIGS. 3a to 5b , the course of laser light in awaveguide having solely straightly extending inner faces and theinventive waveguide 20 are compared. At this, FIGS. 3a, 4a and 5a referto the waveguide with straight inner faces and thus to a straight course3 of laser light. The FIGS. 3b, 4b and 5b are related to an embodimentof the inventive waveguide 20 and thus to an elliptically-shaped course5 of light. Further, the behavior of the laser light after exiting thewaveguide is shown at no displacement, i.e. displacement 0 mm, betweenwaveguide and component (FIG. 3), 0.5 mm displacement (FIG. 4) and 1.0mm displacement (FIG. 5). As can already be seen based on the comparisonof FIGS. 3a and 3b , the laser light can be bundled better in thecomponent 15 by means of the inventive waveguide 20. This effect isextremely measurable with increasing displacement so that in thedepiction of FIG. 5a and upon the usage of the waveguide with straightlyextending inner faces, a major part of the laser light does not reachthe welding zone. In contrast to this, even at a displacement of 1.0 mmbetween component 15 and the embodiment of the waveguide 20, the laserlight reaches the welding zone as shown in FIG. 5b . In the examplesshown the welding zone is arranged in a portion of the T-shapedcomponent 15 which faces away from the waveguide.

Further referring to FIGS. 6b to 7b , the course of laser light afterthe component 15 is shown. Again, the FIGS. 6a and 7a refer to thewaveguide with straight inner faces and the FIGS. 6b and 7b refer to theembodiment of the inventive waveguide 20. It can be clearly seen thatthe laser light with the waveguide 20 is separated in three strandsafter the component 15. This indicates again that a better power densitydistribution of the laser light in the welding zone is present. TheFIGS. 7a and 7b show respectively enlarged sections of FIGS. 6a and 6 b.

Finally and with the respect to FIGS. 8a and 8b , a comparison of theinteraction of laser beams in the respective waveguides is shown. FIG.8a shows the waveguide 7 with straight inner faces as well as an entryend 8 and an exit end 9. FIG. 8b shows the embodiment of the inventivewaveguide 20. Based on this comparison it can be clearly seen that theinteraction between the laser beams in the waveguide 20 is remarkablyreduced compared to the waveguide 7 with straight inner faces, whichcontributes further to the improvement of the waveguide.

An advantage of this embodiment of the waveguide 20 is thus that thebeams of the laser light have less interaction with each other in thewaveguide 20 compared to a waveguide 7 with straight inner faces and thelaser light can be bundled more powerful at the exit end by means of thewaveguide 20. Due to this, an especially homogeneous power densitydistribution can be achieved at the welding seam by means of thewaveguide and a larger tolerance between waveguide 20 and the componentsto be welded can be compensated which increases the simplicity of theusage of an arrangement using the waveguide 20.

Now referring to FIG. 9, an embodiment of an arrangement 100 for plasticwelding with an embodiment of a second negative waveguide 120 accordingto the present invention is shown in perspective sectional view. In thearrangement 100, laser light is guided via a plurality of preferablyflexible light guides 110 to the waveguide 120. The light guides 110 areconnected at an entry end 122 with the waveguide 120, as shown in FIG.11. The laser light is guided through the waveguide 120 to thecomponents 115 to be welded, one of which is the transmission component117 and the other of which is the absorption component 119. To this end,it is an object of the waveguide 120 to homogenize the laser light fromthe light guides 110 so that the power density distribution of the laserlight in the welding zone or at the welding seam is as uniformly aspossible. As can be especially seen based on FIGS. 11 and 12, uponwelding of the two components 117 and 119, an undercut has to beconsidered which is formed by the protrusion of the absorption component119 into a respective recess of the transmission component 117. For abetter understanding of the following explanations, FIG. 10 shows thecourse 113 of the laser light through the waveguide 120 during operationof the arrangement 100.

Referring to FIGS. 11 and 12, the detailed construction of the waveguide120 is explained. The waveguide 120 comprises the entry end 122 definingan entry face for the laser light and the exit end 124 defining an exitface for the laser light. A first 126 and a second inner face 128 extendbetween the entry end 122 and the exit end 124. The two inner faces 126and 128 are arranged opposite to each other and reflect the laser lightduring operation of the arrangement 100. In other embodiments, thesecond inner face 128 is a straight line between the entry end 122 andthe exit end 124 or consists of a plurality of straight sections. At theembodiment with straight segments as well as at the curved embodiment,it may be that the space between the first 126 and the second inner face128 is not larger as the space at a second inner face 128 extendingstraightly between entry end 122 and exit end 124. A curvature of thesecond inner face 128 is thus convex.

The entry face of the entry end 122 is defined by the plane in which thefirst ends of the first 126 and second inner face 128 are arranged atthe entry end 122 of the waveguide 120. In the embodiment shown, thelaser light enters the waveguide 120 perpendicular to the entry face atthe entry end 122. The exit end 24 with the exit face is defined,analogously to the entry face, by the plane in which the second ends ofthe first 126 and the second inner face 128 are arranged at the exit end124 of the waveguide 120. In the embodiment shown, the exit face and theentry face enclose an angle at about 70°. Generally it is advantageousif the angle enclosed between entry end 122 and exit end 124 is in arange of 30° to 150°, preferably 40° to 120°. The laser light from thelight guide 110 enters the waveguide 120 preferably perpendicular to theentry face.

The waveguide 120 with the entry end 122 and the exit end 124 is adaptedin the embodiment shown to a desired seam contour of the components 115to be welded. The waveguide 120 has thus a rectangular shape withrounded edges and encloses thus the components 115 to be welded, asshown in FIG. 9.

Due to the configuration of the waveguide 120 as negative waveguide 120,a cavity is present between the two inner faces 126 and 128 and the twoinner faces are provided with a reflecting layer. Usually, the negativewaveguide 120 has thus a channel like shape. In case of a positivewaveguide consisting of a solid state, no cavity would be presentbetween the two inner faces, as has been explained initially. At therespective positive waveguide, it is ensured by the choice of theappropriate material that total reflection occurs in the interior of thewaveguide, especially at the inner faces.

A first distance between the entry end 122 and the exit end 124 definesa length L of the waveguide 120. Preferably, this length is not definedby a straight line between entry end 122 and exit end 124 but by a wayof the laser light in the waveguide 120, especially by a guide beamalong a central plane M, is explained below. A second distance betweenthe first 126 and the second inner face 128 defines a thickness D of thewaveguide 120. The thickness D of the waveguide 120 decreasescontinuously form the entry end 122 in the direction of the exit end124. In this way, a further focus effect of the laser light from theentry end 122 in the direction of the exit end 124 is achieved.

As can be especially seen based on FIGS. 9 and 11, the first inner face126 has a continuously curved concave shape. This continuously curvedconcave shape is in the embodiment shown part of a first spiral. Due tothis shaping of the first inner face 126, a radius of the first spiralvaries continuously from a point of origin U₁ of the first spiral to thefirst inner face 126 along the waveguide 120. The point of origin U₁ ofthe first spiral is defined by an intersection of two straight linesspaced apart from each other, extending from the first inner face 126and which are arranged in a common cross-sectional plane of thewaveguide 120. A spiral as two-dimensional figure is generally definedin that the radius varies continuously starting from the point oforigin. This distinguishes the spiral for example from a circle, whereinthe radius is always constant.

In the embodiment shown, the shape of the first inner face 124 is partof a logarithmic spiral which is based on the Fibonacci-sequence. Alogarithmic spiral is defined as a curve, which intersects all beams orstraight lines extending from the point of origin 0 in the same angle α.Thus, in the case of a logarithmic spiral and if a partial section ofthe spiral is present, the point of origin can be determined, in casethe angle α is known. As a spiral is a two-dimensional figure, thewaveguide has to be viewed in cross-section. A direction vector of thestraight line extends in that case from the first inner face in thedirection of the second inner face. In case the shape of the secondinner face is also based on a spiral, such as in the embodiment shown,the direction vector of the respective straight line extends away fromthe first inner face. Exemplarily straight lines G₁₁, G₁₂, G₂₁ and G₂₂,which intersect each other in the respective point of origin U₁ or U₂,are shown for clarity reasons in FIG. 11. The equation of thelogarithmic spiral in polar coordinates are ρ=ae^(kφ) with a>0, whereink=cot(α). The radius of curvature r of the logarithmic spiral is definedas r=√{square root over (1+(cot(α))²)}ρ. The zero point is theasymptotic point of the curve. The length of the curve between the firstend and the second end of the first inner face and/or the second innerface is in the case of the logarithmic spiral

$L = {\frac{\sqrt{1 + k^{2}}}{k}{( {\rho_{2} - \rho_{1}} ).}}$

At a waveguide 120 being already present, this length can be measured.

Other spiral types can be used also. According to an alternative, anArchimedean spiral is used as first spiral. A curve which results from amovement of a point with a constant velocity ν on a beam which revolvesaround the point of origin in a constant angular velocity ω is denotedas Archimedean spiral. The equation of the Archimedean spiral in polarcoordinates is ρ=aφ with

$a = \frac{v}{\omega}$

and a>0. For the radius of curvature r of the Archimedean spiral itapplies

$r = {a{\frac{( {\varphi^{2} + 1} )^{3/2}}{\varphi^{2} + 2}.}}$

In a further alternative, a hyperbolic spiral is used as first spiral.The curve of the hyperbolic spiral consists of two branches which extendsymmetrically to the y-axis. For both branches, the straight line y=a isthe asymptote and the point of origin is asymptotic point. The equationof the hyperbolic spiral in polar coordinates is

$\rho = \frac{a}{\varphi}$

with a>0. For the radius of curvature r of the hyperbolic spiral itapplies

$r = {\frac{a}{\varphi}{( \frac{\sqrt{1 + \varphi^{2}}}{\varphi} )^{3}.}}$

In the embodiment shown, the radius of the first spiral decreasescontinuously from the point of origin U₁ of the first spiral to thefirst inner face 126 along the waveguide 120 from the entry end 122 tothe exit end 124. In another embodiment, the radius increasescontinuously in this course of direction. Based on the angle betweenentry end 122 and exit end 124 which is desired for a respectiveapplication, for example due to undercuts being present at thecomponents 115 to be welded or the available installation space, thedesired section of the spiral can be chosen to realize the concave shapeof the first inner face 126.

Between the first 126 and the second inner face 128, a central plane isdefined, the distance of which is constant with respect to the first 126and the second inner face 128 along the length of the waveguide 120 sothat the second inner face 128 also has a continuously curved shape.This shape of the second inner face 128 is part of a second spiral,especially a second natural spiral, so that a radius of the secondspiral varies continuously from a point of origin U₂ of the secondspiral to the second inner face 128 along the waveguide 120. The pointof origin U₂ is determined analogously to the point of origin U₁ of thefirst spiral, as described above. Due to this configuration, laser lightcan be guided very effectively within the waveguide 120.

A length of the first inner face of the waveguide 120 is in the range of3-times to 4-times, especially of 3.5-times, of a distance between theindividual light guides 110 from the plurality of light guides 110. Inthis way, an especially compact construction of the waveguide can beachieved and a collision of the light guides 110 in corner portions canbe avoided, as schematically shown in FIG. 13.

For the sake of completeness, FIG. 14 shows an overlapping view of awaveguide having straightly extending inner faces and the waveguide 120as it has been described above.

An advantage of the waveguide 120 is that lower energy losses occur inthe interior of the waveguide 120 and the laser light can be guidedespecially effectively through the waveguide 120 to a welding seam.Thereby, and compared to known waveguides, more welding energy isprovided at the weld seam of the components 115, especially if thecomponents have an undercut at the welding seam. Further, and withrespect to a closed angular or cornered shape of the entry end 122 andthe exit end 124, the light guides 110 can be incorporated moreeffectively into an arrangement 100 for laser welding, especially at thecorners, due to the spiral shape of the first inner face as collisionsof the light guides 110 at the corners are reduced.

Now referring to FIG. 15, a flow chart of an embodiment of a weldingmethod is shown. The method for plastic welding, especially for lasertransmission welding, with one of the above described arrangements 1;100 comprises first of all the step of arranging (step A) two plasticcomponents to be welded to each other in a mounting device. Thereafter,the step of creating (step B) laser light by means of a laser lightsource follows. Here, the laser light passes through the light guide110, may be a plurality of light guides 110, and subsequently throughone of the above described waveguides 20; 120. In step C, the welding ofthe plastic components to be welded to each other by means of the laserlight exiting the waveguide 20; 120 occurs.

FIG. 16 shows an embodiment of a manufacturing method of a negativewaveguide. In step i, the providing of a first and a second inner facefor the later waveguide takes place. In a second step ii, an applying ofa reflecting layer onto the first and the second inner face takes place.Alternatively, the first and the second inner face may already beprovided with a reflecting layer. In the third step iii, the first andthe second inner face will be arranged such that they are opposite toeach other. A first end of the first and the second inner face definesan entry end of the waveguide, which defines an entry face for laserlight, and a second end of the first and the second inner face definesan exit end of the waveguide, which defines an exit face for laserlight. A first distance between the entry end and the exit end defines alength of the waveguide and a second distance between the first and thesecond inner face defines a thickness of the waveguide.

Depending on the waveguide 20; 120 to be manufactured, the steps of themanufacturing method vary. In a first alternative and for manufacturingthe waveguide 20, the inner faces will be arranged in step iii such thatthe exit end is arranged opposite to the entry end and a central planeof the waveguide extends centrally from the entry end to the exit end.To this end, the first inner face was provided with a continuouslycurved concave shape or has been brought into such a shape prior to thecoating. A third distance between the first inner face and the centralplane of the waveguide varies in this case continuously from the entryend in the direction of the exit end.

In a second alternative, the first inner face was provided with acontinuously curved concave shape or has been brought into such a shape,which is part of a first spiral, especially a first natural spiral. Aradius of the first spiral varies continuously from a point of origin ofthe first spiral to the first inner face along the waveguide. In thisalternative, step iii is thus omitted.

FIG. 17 shows a flow chart of an embodiment of a manufacturing method ofa positive waveguide according to the invention. Here, in contrast tothe manufacturing method according to FIG. 16, a solid state of a lightguiding material is provided in a first step I. The solid statecomprises an entry end defining an entry face for laser light and anexit end defining an exit face for laser light. Further, the solid statehas a first side face defining a first inner face and a second side facedefining a second inner face. The first and the second inner face arearranged opposite to each other and the solid state consists of amaterial which realizes a total reflection of laser light at the firstand the second inner face. A first distance between the entry end andthe exit end defines a length of the waveguide and a second distancebetween the first and the second inner face defines a thickness of thewaveguide.

Depending on the waveguide to be manufactured, the steps of themanufacturing method differ. In a first alternative and for producing awaveguide, the inner face of which has a shape being part of an ellipse,the exit end is arranged opposite to the entry end and a central planeof the waveguide extends centrally from the entry end to the exit end.The method then comprises as second step II the forming of the firstside face such that the first inner face has a continuously curvedconcave shape so that a third distance between the first inner face andthe central plane of the waveguide varies continuously from the entryend in the direction of the exit end.

In a second alternative and for manufacturing a waveguide, the innerface of which has a shape being part of a spiral, the method comprisesthe third step III of forming the first side face such that the firstinner face has a continuously curved concave shape which is part of afirst spiral, especially a first natural spiral. A radius of the firstspiral varies here continuously from a point of origin of the firstspiral to the first inner face along the waveguide.

While the forms of the invention herein disclosed constitute presentlypreferred embodiments, many others are possible. It is not intendedherein to mention all the possible equivalent forms or ramifications ofthe invention. It is understood that the terms used herein are merelydescriptive, rather than limiting, and that various changes may be madewithout departing from the spirit or scope of the invention.

List of Some Embodiments

1. A negative waveguide for plastic welding, especially for lasertransmission welding, comprising:

an entry end defining an entry face for laser light,

an exit end defining an exit face for laser light as well as

a first and a second inner face which are arranged between the entry endand the exit end, which are arranged opposite to each other and by meansof which laser light can be reflected, wherein

a first distance between the entry end and the exit end defines a lengthof the waveguide and a second distance between the first and the secondinner face defines a thickness of the waveguide, wherein

the exit end is arranged opposite to the entry end and a central planeof the waveguide extends centrally from the entry end to the exit end,and

the first inner face comprises a continuously curved, concave shape sothat a third distance between the first inner face and the central planeof the waveguide varies continuously from the entry end in the directionof the exit end.

2. A positive waveguide for plastic welding, especially for lasertransmission welding, comprising:

an entry end defining an entry face for laser light,

an exit end defining an exit face for laser light as well as

a first and a second inner face which are arranged between the entry endand the exit end, which are arranged opposite to each other and by meansof which laser light can be reflected, wherein

a first distance between the entry end and the exit end defines a lengthof the waveguide and a second distance between the first and the secondinner face defines a thickness of the waveguide, wherein

the exit end is arranged opposite to the entry end and a central planeof the waveguide extends centrally from the entry end to the exit end,and

the first inner face comprises a continuously curved, concave shape sothat a third distance between the first inner face and the central planeof the waveguide varies continuously from the entry end in the directionof the exit end.

3. Waveguide according to embodiment 1 or 2, in which the third distanceincreases or decreases continuously from the entry end in the directionof the exit end.

4. Waveguide according to one of the preceding embodiments, in which thesecond inner face is formed mirror-symmetrically to the first inner faceso that the second inner face has a continuously curved concave shapeand a fourth distance between the second inner face and the centralplane of the waveguide varies continuously from the entry end in thedirection of the exit end.

5. Waveguide according to one of the preceding embodiments, in which thethickness at the entry end is between 8% and 25%, preferably 10% to 20%of the length of the waveguide.

6. Waveguide according to one of the preceding embodiments, in which thethird distance increases from the entry end in the direction of the exitend up to an apex and decreases thereafter, wherein the apex is arrangedwith respect to the length in a range between ¼ and ¾ of the length ofthe waveguide, preferably in a range between ⅓ and ⅔ and especiallypreferred at about ½.

7. Waveguide according to one of the preceding embodiments, in which thethickness at the exit end is equal to the thickness at the entry end.

8. Waveguide according to one of the preceding embodiments, in which thethird distance increases from the entry end in the direction of the exitend up to an apex and decreases thereafter, wherein the thickness in theapex is about 1.2- to 2-times, preferably 1.4 to 1.8-times andespecially preferred 1.6-times the thickness at the entry end.

9. Waveguide according to one of the preceding embodiments, in which thecontinuously curved concave shape of the first inner face is part of anellipse.

10. A negative waveguide for plastic welding, especially for lasertransmission welding comprising:

an entry end defining an entry face for laser light,

an exit end defining an exit face for laser light as well as

a first and a second inner face which are arranged between the entry endand the exit end, which are arranged opposite to each other and by meansof which laser light can be reflected, wherein

a first distance between the entry end and the exit end defines a lengthof the waveguide and a second distance between the first and the secondinner face defines the thickness of the waveguide, and

the first inner face comprises a continuously curved concave shape whichis part of a first spiral, especially a first natural spiral, so that aradius of the first spiral from a point of origin of the first spiral tothe first inner face varies continuously along the waveguide.

11. A positive waveguide for plastic welding, especially for lasertransmission welding comprising:

an entry end defining an entry face for laser light,

an exit end defining an exit face for laser light as well as

a first and a second inner face which are arranged between the entry endand the exit end, which are arranged opposite to each other and by meansof which laser light can be reflected, wherein

a first distance between the entry end and the exit end defines a lengthof the waveguide and a second distance between the first and the secondinner face defines the thickness of the waveguide, and

the first inner face comprises a continuously curved concave shape whichis part of a first spiral, especially a first natural spiral, so that aradius of the first spiral from a point of origin of the first spiral tothe first inner face varies continuously along the waveguide.

12. Waveguide according to one of the embodiments 10 or 11, in which theradius of the first spiral increases or decreases continuously from thepoint of origin of the first spiral to the first inner face along thewaveguide from the entry end in the direction of the exit end.

13. Waveguide according to one of the embodiments 10 to 12, wherein anangle in the range of 30° to 150°, preferably 40° to 120° is enclosedbetween the entry end and the exit end.

14. Waveguide according to one of the embodiments 10 to 13, in which acentral plane is defined between the first and the second inner face,the distance of which is constant to the first and the second inner facealong the length of the waveguide so that the second inner face also hasa continuously curved shape which is part of a second spiral, especiallya second natural spiral, so that a radius of the second spiral from apoint of origin of the second spiral to the second inner face variescontinuously along the wave guide.

15. Waveguide according to one of the embodiments 10 to 14, in which thethickness of the waveguide decreases continuously from the entry end inthe direction of the exit end.

16. Waveguide according to one of the embodiments 10 to 15, wherein theconcave continuously curved shape, which is part of a spiral, is chosenfrom one of the following spiral types: hyperbolic, Archimedean,logarithmic or from a spiral based on the Fibonacci-sequence.

17. A negative waveguide for plastic welding, especially for lasertransmission welding comprising:

an entry end defining an entry face for laser light,

an exit end defining an exit face for laser light as well as

a first and a second inner face which are arranged between the entry endand the exit end, which are arranged opposite to each other and by meansof which laser light can be reflected, wherein

a first distance between the entry end and the exit end defines a lengthof the waveguide and a second distance between the first and the secondinner face defines the thickness of the waveguide, and

the first inner face comprises a continuously curved concave shape whichis part of a first curve.

18. A positive waveguide for plastic welding, especially for lasertransmission welding comprising:

an entry end defining an entry face for laser light,

an exit end defining an exit face for laser light as well as

a first and a second inner face which are arranged between the entry endand the exit end, which are arranged opposite to each other and by meansof which laser light can be reflected, wherein

a first distance between the entry end and the exit end defines a lengthof the waveguide and a second distance between the first and the secondinner face defines the thickness of the waveguide, and

the first inner face comprises a continuously curved concave shape whichis part of a first curve.

19. Arrangement for plastic welding, especially for laser transmissionwelding, comprising:

a laser light source,

a light guide, preferably a plurality of light guides, and

a waveguide according to one of the preceding embodiments 1 to 18,wherein

in the operation of the arrangement the laser light passes from thelaser light source through the light guide and subsequently through thewaveguide.

20. Arrangement according to embodiment 19, using a waveguide accordingto one of the embodiments 10 to 18 as well as a plurality of waveguides,wherein a length of the first inner face of the waveguide is in therange of 3-times to 4-times, especially of 3.5-times, of a distancebetween the individual light guides from the plurality of light guides.

21. Method for plastic welding, especially for laser transmissionwelding, with an arrangement according to one of the embodiments 19 or20, comprising the following steps:

a. arranging two plastic components to be welded to each other in amounting device,

b. creating laser light by means of a laser light source, wherein thelaser light passes through the light guide, preferably a plurality oflight guides, and subsequently through a waveguide according to one ofthe embodiments 1 to 18, and

c. welding the plastic components to be welded to each other by means ofthe laser light exiting the waveguide.

22. Manufacturing method of a negative waveguide according to one of theembodiments 1, 3 to 9 in combination with 1, 10, 12 to 16 in combinationwith 10, or 17, comprising the steps:

a. providing a first and a second inner face,

b. applying a reflecting layer on the first and the second inner face,

c. arranging the first and the second inner face such that they areopposite to each other, wherein

d. a first end of the first and the second inner face define an entryend of the waveguide, which defines an entry face for laser light, and asecond end of the first and the second inner face define an exit end ofthe waveguide, which defines an exit face for laser light, wherein

e. a first distance between the entry end and the exit end defines alength of the waveguide and a second distance between the first and thesecond inner face defines a thickness of the waveguide, wherein

f1. the exit end is arranged opposite to the entry end and a centralplane of the waveguide extends centrally from the entry end to the exitend while the first inner face has a continuously curved concave shapeso that a third distance between the first inner face and the centralplane of the waveguide varies continuously from the entry end in thedirection of the exit end or

f2. the first inner face has a continuously curved concave shape whichis part of a first spiral, especially a first natural spiral so that theradius of the first spiral varies continuously from a point of origin ofthe first spiral to the first inner face along the waveguide or

f3. the first inner face has a continuously curved concave shape whichis part of a first curve.

23. Manufacturing method of a positive waveguide according to one of theembodiments 2, 3 to 9 in combination with 2, 11, 12 to 16 in combinationwith 11, or 18, comprising the steps:

a. providing a solid state of a light guiding material, wherein thesolid state comprises an entry end defining an entry face for laserlight and an exit end defining an exit face for laser light, wherein

b. the solid state has a first side face defining a first inner face anda second side face defining a second inner face wherein the first andthe second inner face are arranged opposite to each other and the solidstate consists of a material which provides a total reflection of laserlight at the first and the second inner face while

c. a first distance between the entry end and the exit end defines alength of the waveguide and a second distance between the first and thesecond inner face defines a thickness of the waveguide, wherein

d1. the exit end is arranged opposite to the entry end and a centralplane of the waveguide extends centrally from the entry end to the exitend and the method comprises the step: forming the first side face suchthat the first inner face has a continuously curved concave shape sothat a third distance between the first inner face and the central planeof the waveguide varies continuously from the entry end in the directionof the exit end or

d2. the method comprises the further step of: forming the first sideface such that the first inner face has a continuously curved concaveshape which is part of a first spiral, especially a first naturalspiral, so that a radius of the first spiral from a point of origin ofthe first spiral to the first inner face varies continuously along thewaveguide or

d3. the method comprises the further step of: forming the first sideface such that the first inner face has a continuously curved concaveshape which is part of a first curve.

1. A positive waveguide for plastic welding, comprising: an entry enddefining an entry face for laser light, an exit end defining an exitface for laser light as well as a first and a second inner face whichare arranged between the entry end and the exit end, which are arrangedopposite to each other and by means of which laser light can bereflected, wherein a first distance between the entry end and the exitend defines a length of the waveguide and a second distance between thefirst and the second inner face defines a thickness of the waveguide,wherein the exit end is arranged opposite to the entry end and a centralplane of the waveguide extends centrally from the entry end to the exitend, and the first inner face comprises a continuously curved, concaveshape so that a third distance between the first inner face and thecentral plane of the waveguide varies continuously from the entry end inthe direction of the exit end.
 2. Waveguide according to claim 1, inwhich the third distance increases or decreases continuously from theentry end in the direction of the exit end.
 3. Waveguide according toclaim 1, in which the second inner face is formed mirror-symmetricallyto the first inner face so that the second inner face has a continuouslycurved concave shape and a fourth distance between the second inner faceand the central plane of the waveguide varies continuously from theentry end in the direction of the exit end.
 4. Waveguide according toclaim 1, in which the thickness at the entry end is between 8% and 25%of the length of the waveguide.
 5. Waveguide according to claim 1, inwhich the third distance increases from the entry end in the directionof the exit end up to an apex and decreases thereafter, wherein the apexis arranged with respect to the length in a range between ¼ and ¾ of thelength of the waveguide.
 6. Waveguide according to claim 1, in which thethickness at the exit end is equal to the thickness at the entry end. 7.Waveguide according to claim 1, in which the third distance increasesfrom the entry end in the direction of the exit end up to an apex anddecreases thereafter, wherein the thickness in the apex is about 1.2 to2-times the thickness at the entry end.
 8. Waveguide according to claim1, in which the continuously curved concave shape of the first innerface is part of an ellipse.
 9. A positive waveguide for plastic welding,comprising: an entry end defining an entry face for laser light, an exitend defining an exit face for laser light as well as a first and asecond inner face which are arranged between the entry end and the exitend, which are arranged opposite to each other and by means of whichlaser light can be reflected, wherein a first distance between the entryend and the exit end defines a length of the waveguide and a seconddistance between the first and the second inner face defines thethickness of the waveguide, and the first inner face comprises acontinuously curved concave shape which is part of a first spiral,especially a first natural spiral, so that a radius of the first spiralfrom a point of origin of the first spiral to the first inner facevaries continuously along the waveguide.
 10. Waveguide according toclaim 9, in which the radius of the first spiral increases or decreasescontinuously from the point of origin of the first spiral to the firstinner face along the waveguide from the entry end in the direction ofthe exit end.
 11. Waveguide according to claim 9, wherein an angle inthe range of 30° to 150° is enclosed between the entry end and the exitend.
 12. Waveguide according to claim 9, in which a central plane isdefined between the first and the second inner face, the distance ofwhich is constant to the first and the second inner face along thelength of the waveguide so that the second inner face also has acontinuously curved shape which is part of a second spiral, especially asecond natural spiral, so that a radius of the second spiral from apoint of origin of the second spiral to the second inner face variescontinuously along the wave guide.
 13. Waveguide according to claim 9,in which the thickness of the waveguide decreases continuously from theentry end in the direction of the exit end.
 14. Waveguide according toclaim 9, wherein the concave continuously curved shape, which is part ofa spiral, is chosen from one of the following spiral types: hyperbolic,Archimedean, logarithmic or from a spiral based on theFibonacci-sequence.
 15. A positive waveguide for plastic welding,comprising: an entry end defining an entry face for laser light, an exitend defining an exit face for laser light as well as a first and asecond inner face which are arranged between the entry end and the exitend, which are arranged opposite to each other and by means of whichlaser light can be reflected, wherein a first distance between the entryend and the exit end defines a length of the waveguide and a seconddistance between the first and the second inner face defines thethickness of the waveguide, and the first inner face comprises acontinuously curved concave shape which is part of a first curve. 16.Arrangement for plastic welding, comprising: a laser light source, alight guide, preferably a plurality of light guides, and a waveguideaccording to claim 1, wherein in the operation of the arrangement thelaser light passes from the laser light source through the light guideand subsequently through the waveguide.
 17. Arrangement for plasticwelding, comprising: a laser light source, a light guide, preferably aplurality of light guides, and a waveguide according to claim 9, whereinin the operation of the arrangement the laser light passes from thelaser light source through the light guide and subsequently through thewaveguide.
 18. Arrangement according to claim 17, using a plurality ofwaveguides, wherein a length of the first inner face of the waveguide isin the range of 3-times to 4-times of a distance between the individuallight guides from the plurality of light guides.
 19. Arrangement forplastic welding, comprising: a laser light source, a light guide,preferably a plurality of light guides, and a waveguide according toclaim 15, wherein in the operation of the arrangement the laser lightpasses from the laser light source through the light guide andsubsequently through the waveguide.
 20. Arrangement according to claim19, using a plurality of waveguides, wherein a length of the first innerface of the waveguide is in the range of 3-times to 4-times of adistance between the individual light guides from the plurality of lightguides.